Conventional projectors are generally relatively large, heavy and sensitive, so that they are not suited for mobile use. In addition, such devices have a comparatively high energy consumption and the colors produced sometimes appear pale, for example, when sunlight strikes the projection surface.
Technologies which may be used in miniaturized projectors include the so-called laser scanners or scanning laser projectors. In laser scanners, laser beams emitted by laser diodes are moved in such a way that they scan a projection surface pixel by pixel. A color image may be produced by superimposing laser beams of differing colors and by the targeted, time-dependent pixel by pixel projection and non-projection of laser beams. Scanning passes may take place with such a high repetition frequency that to the human eye, an overall image forms, similar to the scanning of the luminescence layer of a cathode ray tube television with an electron beam. Such laser scanners are small and produce images with bold colors. In addition, they operate energy-efficiently, since a laser beam is switched on only if it is actually needed for the projection.
Miniaturized laser scanners, for example, so-called pico projectors, may be installed, for example, in mobile telephones, tablet PCs and in other mobile terminals, or may be designed as mobile telephones, tablet-PCs or other mobile terminals. Projectors are normally controlled with special remote controllers or by pressing buttons on an input surface. Alternatively, it is also known, however, to control the laser scanner using gestures represented as objects introduced in the beam area of the laser scanner. For this purpose, the backscattered light or laser light from the object, for example, from a hand, is detected and based on this a control gesture is determined. This may take place over time, in particular, over multiple projected overall images, as a result of which, for example, a movement of the hand may be detected and interpreted as a control gesture. A hand introduced from the left into the beam area of the laser scanner and pulled out again, for example, may be interpreted as a control gesture for turning to a subsequent photo of a slide show.
In DE 10 2012 206 851 A1, a method and a device are described for ascertaining a gesture carried out in the light cone of a projected image. In this case, all pixels and in each case one or multiple parameter values of the pixels of the projected image are detected and the parameter values are each compared to one parameter comparison value and assigned to a pixel set as a function of the result of the comparison. Based on the assigned pixel set, the gesture carried out in the light cone of the projected image is ascertained.
When ascertaining gestures in the light cone or beam area of a projector or laser scanner, there is normally an evaluation of differences in luminous intensity, which result from an object, for example, a hand, being introduced into the beam area, whose reflection properties for the emitted light differ from the reflection properties of the intended projection surface. The speed and accuracy with which a particular gesture is detected is usually influenced by the image to be projected. For example, a purely black image could be “projected,” i.e., no light emission would take place, over a longer period of time, as a result of which no gestures could be detected for the corresponding duration.